Metalized recording carrier for recording instruments, and method of its manufacture

ABSTRACT

To prevent the formation of scratches, surface discontinuities, slide tracks or striations, for example due to sliding of electrodes (20) over the metal layer (12) of a metalized recording medium, a protective surface coating (13) of low-friction sliding protective material is applied in the form of discontinuous islands over the metal layer (12). The discontinuities permit electrical contact between the electrode (20) and the metal layer (12) although the protective surface coating (13) has insulating properties. The coating (13) may be polymerized hexamethyl-disiloxane, hexafluoropropylene, or Teflon, polymerized, preferably in hot cathode glow discharge; or a metallic soap. The protective layer is hydrophobic in the form of islands of a thickness of between 10 -9  m to 10 -7  m, preferably about 1 to 2×10 -8  m, thus protecting the underlying metal layer (12) against damage by the electrode (20), and attack by moisture or dampness from the ambient atmosphere. A surface portion can be rendered hydrophilic to permit writing on the recording paper by a felt pen, with aqueous ink or the like.

The present invention relates to recording carriers for recordinginstruments, and particularly to a recording carrier in web-like form,for example of paper or plastic, which has a metallic coating which,under the influence of electrical voltage applied across an electrode,is capable of being burned off, leaving a trace at the burn-offposition, and to a method of its manufacture.

BACKGROUND

Various types of recording paper based on removal of a top cover layerof a metal, typically aluminum, under influence of applied electricalsignals, have been proposed.

One such recording carrier is described in German Pat. No. 1 945 939.The outer metal layer is aluminum, applied to a web-like or strip ortape-like paper carrier. The chemical integrity of the metal layer isimproved if some proportion of the aluminum of the coating is convertedinto aluminum oxide or aluminum oxyhydrate. The permanence and stabilityof the coating are thereby enhanced.

Another way of enhancing the permance and stability of the recordingcarrier is described in Swiss Pat. No. CH-PS 301 000, in which a metalcoating, not further described, is covered with a thin cover coatingapplied thereover. Such a thin protective cover coating can be obtainedby a layer of quartz or paraffin, applied by condensation from a vaporphase. Oils as protective layers in a molecular thickness can also beapplied by vapor deposition. It has also been proposed to use a lacquercoating of polystyrene as a protective coating.

It has been proposed to protect optical components such as mirrors,lenses or the like, against chemical and/or mechanical damage byproviding a protective layer over the optical elements (see GermanPatent Disclosure Document DE-OS 22 63 480). Such a protective layer toprotect the optical components or devices with respect to mechanical orchemical influences is a hydrophobic protective layer or coating appliedto a substrate forming the optical element. The hydrophobic protectivelayer is obtained by precipitation and polymerization of polysiloxane inan electrical glow discharge. An organo-silicon compound is introducedinto a vacuum vessel in the form of a vapor, and polymerized by a glowdischarge on the substrate. This protective coating has the advantage ofrelatively high mechanical hardness and good adhesion, thus providing animproved protective coating with respect to mechanical protection of thesubstrate while, additionally, having a decreased coefficient offriction with respect to elements or devices sliding thereover, that is,providing for good sliding properties over the thus protected opticalcomponent.

The purpose of the protective coating, however made or constituted, isintended to increase the stability and permanence of the actualrecording layer. Ideally, the metal recording layer should be protectedagainst decomposition due to ambient humidity or moisture in the air andagainst abrasion due to travel of the electrodes thereover, which mayleave scratches or tracks.

THE INVENTION

It is an object to provide a recording substrate, typically paper, witha metal coating capable of being burned off by an electrode slidingthereover in which the metal coating is effectively protected againstmechanical and/or chemical deterioration.

Briefly, the recording medium uses a substrate carrier or base,typically made of paper, or made of a plastic or the like, with acoating thereover which is made of a metal capable of being burned offwhen subjected to an electrical discharge by an electrode applied overthe metal. A contrasting layer may be interposed between the metal,typically aluminum, and the substrate carrier.

In accordance with the invention, a low-friction sliding surface layeris applied over the metal layer to prevent deterioration of therecording medium as well as of electrodes applied to the top layer whichglide thereover.

The recording medium has the advantage that it has, compared to priorart media, an entirely different coefficient of friction with respect toelectrodes sliding thereover, while also effectively protecting themetal coating against mechanical damage. The protection of the top layeris particularly important since damage of the recording carrier in theform of scratches, striations, or slide or draw tracks by the electrodesin those locations where they do not burn out the top layer areeffeciently prevented. Thus, the contrast of the trace of the recordingmade and areas beneath the electrode which do not have a recordingburn-off spot, but which are beneath the electrode and carriedtherealong by a paper transport, are not impaired due to the mechanicalabrasion of the electrode against the metal layer. Additionally, themetal coating or layer, and hence the overall recording medium, has asubstantially longer shelf life, and aging influences due to storage andambient atmospheric conditions are effectively inhibited.

In accordance with a feature of the invention, the layer applied to themetal coating is a hydrophobic layer, thus effectively preventingdeterioration of the underlying metal by ambient atmospheric humidity ormoisture. If it is desired to additionally permit manual writing orprinting on the carrier, after it has been metalized and protected witha hydrophobic layer, a post-treatment with oxygen permits formation of ahydrophilic surface region in the hydrophobic protective layer. Thishydrophilic surface facilitates manual application of indicia or legendsby aqueous inks, with felt pens, and the like.

The hydrophobic layer can be applied in the form of vapor-deposited andpolymerized hexamethyldisiloxane; metallic soaps may also be used,providing for coatings with hydrophobic characteristics.

DRAWINGS

The FIGURE shows a recording carrier with a protective layer on thesurface of a metal coating, and, highly schematically, an electrodethereover capable of forming a burning visible recording trace in therecording carrier.

A web or sheet-like carrier 10, made of paper or plastic, for example apolyester such as Mylar®, forms the substrate or carrier for therecording medium. The carrier 10 has a contrast layer 11 applied theretoin order to improve the resistance against corrosion of the entirerecord carrier and to provide for optical contrast between recorded andnon-recorded surface areas. The contrast layer 11 may, for example, be alacquer or an ink. A metal layer 12, typically aluminum, is applied overthe contrast layer 11. The metallic layer is vacuum-deposited; ratherthan aluminum, it may be of zinc and/or cadmium. Scratches, slidetracks, and other damage to the surface, marring its visual continuity,are prevented by forming a sliding or low-friction layer 13 over themetal coating 12. Such scratches and sliding tracks and the like can becaused by drawing the recording carrier beneath an electrode 20 in thedirection of the arrow 24. Electrode 20 of spring wire and the like isconnected to a source of positive voltage 21, the metal layer 12 beingconnected to the negative terminal 22, shown as a ground, chassis orframe connection. Grounding can be obtained, for example, by passing aroller over the carrier, in electrical contact with the aluminum layer12, or connecting an end portion thereof to a grounded clamp. Dependingon the energization of terminal 21, as shown schematically by apulse-like signal 23, selected areas of the metal coating 12 will beburned off as the record carrier 24 is drawn beneath the electrode inthe direction of the arrow 24. In those regions where the carrier moveswithout a signal being applied, however, as illustrated for example bythe gap in the signal 23, the electrode 20 may cause scratches or othersurface imperfections in the recording surface of the carrier, thusdetracting from the legibility of those areas where the metal coating 12has been burned off. In accordance with the present invention, thesliding or low-friction layer 13 prevents damage to the metal layer 12by providing a low-friction sliding surface for the electrode 20. Thelayer 13 is not continuous, but rather is a sequence of dots or islandsof low-friction material. Due to the small sizes of the gaps betweenislands, it may visually appear continuous. It provides a slidingsurface for the electrode 20 to glide thereover.

In accordance with a feature of the invention, the sliding layer 13 ismade this way: A hydrophobic layer 13 is applied, preferably made ofpolymerized hexamethyldisiloxane (HMDS); other layers may be used, forexample a layer made of a polymerized hexafluoropropylene (HPF), orpolytetrafluoroethylene (PTFE), customarily known as Teflon®. Thevarious sliding or low-friction layers can be readily applied from thevapor phase by deposition on the metallic layer 12 and polymerization ina glow discharge. Polymerization can be obtained by either a glowdischarge due to high-voltage application between electrodes, or by aglow discharge using a heated emitting electrode which operates in a gaswhich amplifies the discharge. Use of a thermally generated glowdischarge is preferred, since the operating voltages required aresubstantially less than when using cold-cathode discharge, and the loweroperating voltage results in apparatus requiring less insulation due tothe lower operating voltage in the metal vapor deposition apparatus, andthus facilitating control of the process.

For some applications it may be desirable to permit writing on the layer13 by ink, felt pens, or the like, on the coated recording medium. Topermit such writing, the surface of the layer 13 is renderedhydrophilic. This can be achieved by exposing the surface to oxygentowards the end of the polymerization process. A top surface which isinorganic and similar to quartz will then form on the protective layer.This top surface will accept aqueous ink, writing with a felt pen, orthe like.

In accordance with another feature of the invention, the low-frictionlayer 13 is a hydrophobic metal soap layer. It has been found byexperimentation that such a layer has good permanence and excellentsliding or gliding characteristics. Metal soaps normally are availablein colloidal form and are applied in a separate process on a previouslyvapor deposited metal layer 12.

The recording medium is particularly suitable having an aluminumrecording layer, using paper for the substrate 10. With respect topreviously used recording carriers, it has substantially increasedresistance against scratching, slide tracks, or other marring orimpairment of the surface, which may occur due to the contact with theelectrodes 20, or deposits which build thereon, and which interfere withthe overall visibility of the recording being made. The electrodeseasily slide over the recording carrier regardless of the voltagecondition at terminals 21, 22, that is, regardless of whether they areenergized or not. In dependence on the surface characteristics, and thequality of the surface over which the electrodes 20 slide, the surfaceis more or less affected by the electrodes, regardless of whether theycarry current or not, and, if the surface is subject to deterioration,striations or scratches may result. Layer 13 permits easy sliding of theelectrodes over the substrate.

In accordance with a feature of the invention, the low-friction orsliding layer 13 can be applied to the metal coating 12 simultaneouslyor in connection with an already present step in making the recordingcarrier. Thus, the low-friction layer 13 can be applied in the vapordepositing apparatus itself, immediately downstream, in the direction ofmanufacture of the metal coating, behind the vapor depositing stationfor the metal coating 12; this is a preferred form; alternatively, thecoating 13 can be applied in a spooling station, in combination with atesting station, with a cutting station, or a packaging station. Thevarious apparatus components are well known and are constructed in asuitable manner to permit exposure of the surface 13 to the vaporizedmaterial of the substance selected to form the layer 13, andpolymerization thereof, for example by a thermally assisted glowdischarge.

In a typical example, the paper layer 10 may have a thickness of betweenabout 0.05 to 0.1 mm, over which a lacquer coating 11 of about 0.001 to0.01 mm is applied, using carbon black as a contrast pigment. The rangeis not critical, and the lower thickness is preferred. The aluminumlayer may be between about 0.01 and 0.1 μm, preferably between about0.05 to 0.1 μm.

The sliding or low-friction top layer 13 may have a thickness of betweenabout 10⁻⁹ to 10⁻⁷ m, preferably between about 10⁻⁸ m to 2×10⁻⁹ mthickness. The above-given figures relate to average thickness. Thelayer 13 is not generally a continuous layer but, rather, isinterrupted, that is, it has pores therebetween. The actual top or peakof the layer 13 above the underlying coating 11 may extend over theaverage thickness which is generally shown; the extension above theaverage thickness is indicated at 13' in the FIGURE, Molecules ofsliding material may well have a size which exceeds the minimum size ofthe average layer thickness, that is, the molecules themselves may havea size greater than 10⁻⁹ m in diameter, that is, extend to the peak ofthe dimension 13', as shown in the drawing. It is to be understood, ofcourse, that the drawing is highly schematic, and the generally uniformthickness relates to the average thickness for ease of illustration. Theinterruptions or gaps between the molecules, or strings of molecules, orislands of molecules forming the layer 13 will also permit discharge ofelectric energy from the electrode 20 to the underlying metal layer 12without having to overcome the dielectric insulation resistance of thelayer 13 which, in some embodiments, may be an excellent insulator, suchas Teflon, for example. A suitable operating voltage between terminals21, 22 is between about 15-60 V.

Metallic soaps have been found to be eminently suitable as a materialfor the coating 13. A suitable metallic soap is, for example, aluminummetallic soap, derived from the vapor-deposited aluminum conductivelayer, or mechanically applied. Sodium soap also has been found to beeminently suitable. Sodium soap may be applied from the solid phase witha layer thickness of about 10⁻⁸ m. Application from the solid phase isdesirable; application from the liquid phase will lead to a closedcontinuous layer 13--contrary to that shown in the FIGURE of thedrawing, so that recording difficulties will arise when the recordingmedium is to be employed for its intended purpose. Interruption of thecontinuity of the layer 13 substantially facilitates the recordingoperation. In the drawing, electrode 20 is shown only schematically,and, of course, not to scale with respect to the layer 13 and the peaks13'.

Although the layer 13 is not continuous, the underlying metallic layer12 is protected against mechanical abrasion due to the presence of theelectrode, so that scratches, drawn lines and tracks upon engagement ofthe electrode 20 with the top of the medium are effectively prevented.The layer, although not continuous, also has good protective propertieswith respect to ambient humidity and moisture due to the extremely smallinterruptions or gaps between the islands forming the layer 13. Theextreme thinness of layer 13 permits electrical discharge from theelectrode 20 to the metal layer 12 through the gaps between the islandsof the layer 13.

Metallic soaps can be defined, for example, as a salt of amonocarboxylic acid, as a higher fatty acid, resin acid, naphthenic acidwith a bivalent or trivalent metal, for example calcium, cobalt, zinc,copper, lead, aluminum, sodium, that typically is insoluble in water butsoluble in benzine. Other uses for such metallic soaps are in lubricantsor driers and for water-proofing.

We claim:
 1. Metalized recording medium for recording instruments of theburn-out recording type upon being subjected to an electrical dischargefrom an electrode (20) having a contacting surface which is being passedover the surface of the medium, comprisinga substrate carrier (10); ametal layer (12) supported by the carrier and of a thickness permittingburning-off of the metal layer when positioned beneath an energizedelectrode (20); and a low-friction surface layer applied over said metallayer, wherein, in accordance with the invention, the low-friction slidesurface layer (13) is formed, prior to contact with an energizedelectrode, of discontinuous islands .[.smaller than the contactingsurface of the electrode (20).]. to permit easy gliding of the electrode(20) over the surface of the carrier without marring or scratching orleaving tracks on the carrier upon relative movement between the carrierand the electrode while providing for electrical connection of theelectrode with said metal layer (12).
 2. Recording medium according toclaim 1, wherein low-friction slide the layer (13) is a hydrophobicsurface layer.
 3. Recording medium according to claim 2, wherein thesurface layer (13) comprises polymerized hexamethyldisiloxane. 4.Recording medium according to claim 2, wherein the hydrophobic layer(13) comprises polymerized hexafluoropropylene.
 5. Recording mediumaccording to claim 2, wherein the hydrophobic low-friction slide surfacelayer (13) comprises polytetrafluoroethylene.
 6. Recording mediumaccording to claim 2, wherein the low-friction slide surface layer (13)has an upper surface portion which is hydrophilic.
 7. Recording mediumaccording to claim 6, wherein the hydrophilic surface portion comprisesan oxygenated surface portion.
 8. Recording medium according to claim 1,wherein the low-friction slide surface layer (13) comprises a layer of ametal soap.
 9. Recording medium according to claim 1, wherein thesubstrate carrier (10) comprises at least one of the materials selectedfrom the group consisting of: paper; plastic; and the metal layer (12)comprises a vapor-deposited metal layer comprising at least one of thematerials of the group consisting of: aluminum, cadmium; zinc; andhaving a thickness in the order of about 0.01 to 0.1 μm.
 10. Recordingmedium according to claim 1, wherein the low-friction slide surfacelayer (13) comprises a glow discharge polymerized vapor-deposited layerapplied over the metal layer (12).
 11. Recording medium according toclaim 1, wherein the low-friction slide surface layer (13) has anaverage thickness of between about 10⁻⁹ to 10⁻⁷ m.
 12. Recording mediumaccording to claim 1, wherein the low-friction slide surface layer (13)has an average thickness of between about 1 to 2×10⁻⁸ m.
 13. Method ofmaking a metalized recording medium for recording instruments of theburn-out recording typeas claimed in claim 1 having a substrate carrier(10) and comprising the steps of: introducing the carrier into a closedvessel; vapor-depositing a metal layer (12) on the carrier of athickness permitting burning-off of the deposited metal layer, whenpositioned beneath an energizing electrode; and applying a low-frictionprotective slide surface layer (13) immediately behind the vapordeposition station in the form of discontinuous islands .[.smaller thanthe contacting surface of the electrode.]. within said vessel on thevapor-deposited metal layer.
 14. Method according to claim 13, whereinthe step of applying the low-friction slide surface layer comprisesdepositing a polymerizable material from the vapor phase on the metallayer;and exposing the vapor-deposited protective layer to a glowdischarge to polymerize said protected low-friction slide surface layer(13).
 15. Method of making a metalized recording medium for recordinginstruments of the burn-out recording typeas claimed in claim 1 having asubstrate carrier (10) and comprising the steps of: introducing thecarrier into a closed vessel; vapor-depositing a metal layer (12) on thecarrier of a thickness permitting burning-off of the deposited metallayer, when positioned beneath an energizing electrode; spooling andtesting said metal layer at a spooling and testing station; and applyinga low-friction protective slide surface layer (13) in the form ofdiscontinuous islands .[.smaller than the contacting surface of theelectrode.]. at said spooling and testing station.
 16. Method of makinga metalized recording medium for recording instruments of the burn-outrecording typeas claimed in claim 1 having a substrate carrier (10) andcomprising the steps of: introducing the carrier into a closed vessel;vapor-depositing a metal layer (12) on the carrier of a thicknesspermitting burning-off of the deposited metal layer, when positionedbeneath an energizing electrode; cutting the carrier to a predeterminedformat at a cutting station; and applying a low-friction protectiveslide surface layer (13) in the form of discontinuous islands .[.smallerthan the contacting surface of the electrode.]. at said cutting station.17. Recording medium according to claim 1, wherein the material of thelow-friction slide surface layer (13) is electrically insulating. 18.Recording medium according to claim 1, wherein said low-friction slidesurface layer (13) is formed with pores to provide for gaps orinterruptions between said islands.
 19. Recording medium according toclaim 1, wherein said islands are formed by strings or islands ofmolecules of the material of said low-friction slide surface layer.